Digital media services provide subscribers with access to downloadable video information, such as television programs, movies, audio programs and text-based information streams. Typically, subscribers selectively access such services via a connection to a communication network. In the network, the services are provided from one or more information sources. Routers in the network are coupled to both the sources and the subscribers; the routers provide linking interfaces to enable the sources to transmit their services to the intended subscribers in the network.
Generally, when services are provided to a specific list of subscribers in a network, a multicast transmission is used. Therein, one router transmits messages to multiple destinations. For multicast transmissions, a router requires group information identifying members of a group which are to receive a specified multicast transmission. In an Internet Protocol (IP) v4 network, Internet Group Management Protocol (IGMP) commands are sent from hosts to routers in the network to manage IP multicast transmissions. IGMP is an evolving protocol. The Internet Engineering Task Force (IETF) has published numerous specifications for IGMP, as its standards evolve, including: RFC 1112, entitled “Host Extensions for IP Multicasting”; RFC 2236, entitled “Internet Group Management Protocol, Version 2”; and RFC 3376 entitled “Internet Group Management Protocol, Version 3”. All three specifications are incorporated herein by reference. IGMP, version 2 is designed to be interoperable with Protocol Independent Multicast-Sparse Mode (PIM-SM) multicasting. IGMP, version 3 adds the capability for Protocol Independent Multicast-Single Source Multicast (PIM-SSM) multicasting. PIM-SSM provides simplified processing in both the data plane and the control plane over PIM-SM. Unfortunately, some mapping constructs of IGMP v3 are not compatible with IGMP v2. This is problematic when a legacy host, which recognizes only IGMP version 2 protocol commands, is connected to a network which utilizes PIM-SSM.
Therefore, a need exists for a method and apparatus for supporting multicast group transmissions that provides PIM-SSM compatibility with legacy protocols.